The present invention generally relates to particle-reinforced composite materials and methods for the production. More particularly, this invention relates to a process of producing composite materials that utilizes an in situ reaction process to produce a uniform dispersion of a fine particulate reinforcement phase.
There is considerable interest in processes for producing particulate-reinforced metal matrix composite (MMC) components for a large array of metals and alloys for the purpose of increasing their strength, hardness, and/or wear resistance. As nonlimiting examples, aluminum alloys and magnesium alloys are relatively lightweight materials that have found increased applications in the defense and transportation industries, and the ability to increase desired properties of these alloys could further expand their uses in these industries.
In-situ methods for forming small particles in molten metals and alloys are the most cost effective methods for making particulate-reinforced metal matrix composites. One of the in-situ methods under development involves the addition of large particles in a molten metal (the term “metal” is used herein to refer to individual metals as well as their alloys). The particles react with the molten metal to form new particles containing elements from the large particles and the molten metal. The newly formed particles are usually smaller but the morphology of these new particles varies depending on the reaction kinetics. As a result, limited types of spherical particles have been formed in molten metals. Furthermore, the reactions occur at extremely high temperatures, and therefore it can be difficult to use these processes to produce high quality, lightweight matrix composites, for example, aluminum or magnesium matrix composites.
Liquid stirring techniques are often employed for dispersing the resultant particles (or the added particles) in the melt. The stirring method is a cost-effective method compared to many other methods, such as ball-milling and chemical deposition. However, stirring methods are typically only capable of dispersing particles larger than ten micrometers. Liquid stirring methods are known to be not generally effective for separating particles smaller than ten micrometers from their agglomerates, breaking up individual particles from their clusters formed during a self-propagating high-temperature synthesis (SHS) process, and breaking up the reaction products (smaller particles) during the chemical reaction of an in-situ direct melt process. It is believed that this limitation is attributable to the insufficiency of shear stresses generated by melt stirring.
On the other hand, high-intensity ultrasonic vibration has been used for separating nano-size particles from their agglomeration in order to disperse these tiny particles in the melt for forming nanocomposites.